1. Field of the Invention
The present invention pertains to a liquid crystal display, and more particularly to a liquid crystal display comprising multiple cells stacked together and the manufacturing method therefor.
2. Description of the Related Art
Research and development of displays using liquid crystal has been actively pursued in recent years. In particular, displays using a chiral nematic liquid crystal composition, which exhibits a cholestric phase at room temperature and which is obtained by adding a chiral agent to nematic liquid crystal, as well as guest-host type displays using nematic liquid crystal to which a dichroic pigment is added, have been drawing attention.
In a liquid crystal display including a liquid crystal composition that exhibits a cholesteric phase, display is performed by switching the liquid crystal back and forth between a planar state (selective reflection state) and a focal conic state (light scattering state) by applying a high or low pulse voltage. Where a material comprising liquid crystal to which a multichroic pigmentxe2x80x94such as a dichroic pigmentxe2x80x94is added is used for the liquid crystal composition, display is performed by changing the direction of the axes of the liquid crystal molecules when voltage is applied and when voltage is not applied, so that the display alternates between a colored state and a non-colored state.
One method to realize multi-color image display on the displays described above involves a construction in which three cells, which display red (R), green (G) and blue (B), respectively, are stacked. In this case, drive ICs that apply different voltages to the three cells, which display R, G and B, respectively, are needed, resulting in the problem of increased cost. Therefore, a liquid crystal display that has a layered construction having display and drive characteristics appropriate for practical use is not yet available.
The main object of the present invention is to provide an improved liquid crystal display having a that has a layered construction.
Another object of the present invention is to provide a liquid crystal display that is capable of displaying high-quality images.
Still another object of the present invention is to provide a liquid crystal display that is easy to control.
Yet another object of the present invention is to provide a liquid crystal display in which the stacked cells can be driven using a few types of drive ICs so that the cost can be reduced, as well as a method for manufacturing such a liquid crystal display.
To attain at least one of the objects identified above, the liquid crystal display reflecting a first aspect of the present invention comprises a plurality of liquid crystal light modulation layers stacked together, each of said liquid crystal light modulation layers including a liquid crystal composition comprising a liquid crystal compound, wherein at least two of said liquid crystal light modulation layers are substantially have essentially identical maximum drive voltages.
By including at least two liquid crystal light modulation layers that have essentially identical maximum drive voltages, the liquid crystal display can be driven using a few types of drive ICs and its cost may can reduced.
The maximum drive voltages for all of the liquid crystal light modulation layers may be made identical. In this way, the liquid crystal display can be driven using a smaller number of types of drive ICs, which leads to a further reduction in cost.
Moreover, by making the maximum drive voltages for at least two liquid crystal light modulation layers substantially identical, the ranges of drive voltage for these liquid crystal light modulation layers can be made substantially the same, which makes drive control easy.
It is preferred that each liquid crystal light modulation layer be held between a pair of substrates, and that one of the substrates in the pair have scanning electrodes while the other has signal electrodes. The scanning electrodes of at least two liquid crystal light modulation layers may be electrically connected. By electrically connecting the scanning electrodes, the construction of the drive circuit can be simplified.
The same type of signal drive IC may be used for the signal electrodes of at least two liquid crystal light modulation layers. In this way, the construction of the drive circuit can be simplified.
At least one of the substrates may be pliable. By using pliable substrates, the liquid crystal display may be made flexible. In particular, if resin film substrates are used, the liquid crystal display may be made lightweight.
Resin structures may be placed in the light modulation area between the pair of substrates that holds each liquid crystal light modulation layer. By placing resin structures in this way, the distance between the substrates may be accurately maintained and the thickness of the liquid crystal layer may be made uniform. In addition, the substrate distance may be maintained well even if pliable substrates are used, and it is easy to increase the size of the liquid crystal display.
Each liquid crystal light modulation layer may comprise a composite film in which the liquid crystal composition is dispersed in a high-polymer matrix. In this way, the size of the liquid crystal display can be easily increased and a good angle of visibility can be obtained.
The liquid crystal composition may be one that exhibits a cholesteric phase at room temperature. In this case, the liquid crystal display may comprises, as the light modulation layers, three layers, i.e., a liquid crystal layer for blue color that displays blue, a liquid crystal layer for green color that displays green, and a liquid crystal layer for red color that displays red, stacked in that order from the light receiving side (the viewing side).
Each liquid crystal light modulation layer may comprise one that performs display based on the guest-host effect. This type of display can be realized by using a liquid crystal composition comprising nematic liquid crystal to which a multichroic pigment is added as an additive, for example. In this case, by controlling the orientation of the pigment molecules by changing the liquid crystal molecular alignment, the liquid crystal layer may be alternated between a colored state and a non-colored state.
Each liquid crystal light modulation layer may include functional films such as an insulating film and/or an orientation control film, in addition to the liquid crystal layer including the liquid crystal composition. In this case, the maximum drive voltages for at least two liquid crystal light modulation layers may be made substantially identical by adjusting the thickness of the functional films.
In a second aspect of the present invention, a manufacturing method for a liquid crystal display containing a plurality of liquid crystal light modulation layers stacked together, each of said liquid crystal light modulation layers including a liquid, crystal composition comprising a liquid crystal compound, the manufacturing method comprises a step of substantially equalizing maximum drive voltages of at least two of said liquid crystal light modulation layers by adjusting at least one of the following factors:
a thickness of each of said liquid crystal layers contained in the at least two liquid crystal light modulation layers;
a kind of at least one component of each of the liquid crystal compositions included in the at least two liquid crystal light modulation layers;
a dielectric anisotropy of each of the liquid crystal compositions included in the at least two liquid crystal light modulation layers; and
a thickness of each of functional films provided in the at least two liquid crystal light modulation layers.
By appropriately designing at least one of the above mentioned factors, the maximum drive voltages of the at least two liquid crystal layers can be easily made identical, such that the liquid crystal display can be driven using a small number of types of drive ICs, and its cost may be reduced.
According to a third aspect of the present invention, a liquid crystal display comprising a plurality of liquid crystal light modulation layers stacked together, each of said liquid crystal light modulation layers including a liquid crystal layer comprising a liquid crystal composition, wherein at least one of said liquid crystal layers has a thickness different from those of the remaining ones of the liquid crystal layers.
In this liquid crystal display, by making the thickness of the at least one liquid crystal layer different from those of the remaining ones of the liquid crystal layers, the variations in the range of drive voltage that are caused by the fact that the liquid crystal layers are adjusted to modulate light of specific wavelength ranges different each other can be eliminated.
It is preferred that the liquid crystal layers include a pair of liquid crystal layers that have different thicknesses and in which the dielectric anisotropy of the liquid crystal composition in the thicker layer is larger than that in the thinner layer. Because less voltage is required to perform alternation of the liquid crystal layer between a colored state and a non-colored state as the dielectric anisotropy increases, by using this construction, the variations among the liquid crystal layers in terms of the drive voltage range may be accurately eliminated.
The liquid crystal composition included in the liquid crystal layer with a larger dielectric anisotropy may include a liquid crystal compound that has a polar group. For the liquid crystal compound having a polar group, the liquid crystal composition may include at least one compound selected from the following groups: a liquid crystal ester compound, a liquid crystal pyrimidine compound, a liquid crystal cyanobiphenyl compound, a liquid crystal cyanophenylcyclohexane compound, a liquid crystal cyano terphenyl compound, and a liquid crystal difluorostilbene compound.
All of the liquid crystal layers can differ from each other in thickness, and the dielectric anisotropy of the liquid crystal compound in each liquid crystal layer may be different from the others. In this way, the level of freedom in designing the liquid crystal compounds included in the liquid crystal layers increases, and the light modulation characteristics required of each liquid crystal layer can be optimized.
The drive voltage ranges for all of the liquid crystal layers may be made substantially identical as well. By making the drive voltage ranges for all of the liquid crystal layers substantially identical, drive control becomes easy and a common drive IC can be used.
The liquid crystal composition included in each liquid crystal layer may comprise a liquid crystal compound and an additive. For the additive, a substance that includes a compound that has at least one asymmetric carbon may be used. By adding such an additive to nematic liquid crystal as a chiral agent, a liquid crystal composition that exhibits a cholesteric phase at room temperature can be obtained. By changing the amount and type of the chiral agent added, the characteristics of the liquid crystal composition, such as the selective reflection wavelength, can be changed.
If the liquid crystal composition is one that exhibits a cholesteric phase at room temperature, display based on the selective reflection of light of a specific wavelength range may be performed. In addition, multi-color image display may be obtained by using a liquid crystal layer for blue color that displays blue, a liquid crystal layer for green color that displays green and a liquid crystal layer for red color that displays red, stacked in that order from the light receiving side (the viewing side).
A multichroic pigment may be used as an additive to the liquid crystal composition. By using a multichroic pigment, the chromatic purity of the display of the liquid crystal layer can be improved.
Each liquid crystal layer may be driven by using so called the guest-host effect. Such display may be performed by using a liquid crystal composition comprising nematic liquid crystal to which a multichroic pigment is added, for example. In this case, by controlling the orientation of the pigment molecules by changing the liquid crystal molecular alignment, the liquid crystal layer may be alternated between a colored state and a non-colored state.
A color filter may be used between at least one pair of adjacent liquid crystal layers. By using a color filter, the chromatic purity of the display of the liquid crystal layer may be improved and the angle of visibility may be improved.
Each liquid crystal layer is preferably held between a pair of substrates. At least one of the substrates may be pliable. By using pliable substrates, the liquid crystal display may be made flexible. In particular, where resin film substrates are used, the liquid crystal display may be made lightweight.
Resin structures may be placed in the light modulation area between the pair of substrates that hold each liquid crystal layer. By placing resin bodies in this way, the distance between the substrates may be accurately maintained and the thickness of the liquid crystal layer may be made uniform. In addition, the substrate distance may be maintained well even if pliable substrates are used, and it is easy to increase the size of the liquid crystal display.
Each liquid crystal layer may comprise a composite film in which the liquid crystal composition is dispersed in a high-polymer matrix. When this is done, it is easy to increase the size of the liquid crystal display and a good angle of visibility may be obtained.
Functional films may be placed on at least one of the pair of substrates that hold the liquid crystal layer, and the thicknesses of the functional films may be made identical for each liquid crystal layer. In this way, the construction of the substrate having functional films may be made identical from one liquid crystal layer to another, which makes manufacturing easy.
According to a fourth aspect of the present invention, a liquid crystal display comprises a plurality of liquid crystal light modulation layers stacked together, each of said liquid crystal light modulation layers including a liquid crystal layer comprising a liquid crystal composition, wherein at least one of component of each of said liquid crystal layers is different from each other.
By giving all of the liquid crystal layers different liquid crystal compositions, it becomes possible to provide the optimal light modulation characteristics in each liquid crystal layer, which leads to high-quality light modulation for the entire liquid crystal display having a layered construction.
In a fifth aspect of the present invention, a liquid crystal display comprises a plurality of liquid crystal light modulation layers stacked together, each of said liquid crystal light modulation layers including a liquid crystal layer comprising a liquid crystal composition, wherein at least two of said liquid crystal layers have different thicknesses and different liquid crystal compositions.
By having at least two liquid crystal layers with different liquid crystal compositions and thicknesses, the variations in the drive voltage range among the liquid crystal layers may be reduced while ensuring optimal light modulation characteristics.
In this liquid crystal display reflecting the fifth aspect, the liquid crystal layers may include two liquid crystal layers that have different thicknesses and in which the dielectric anisotropy included in the thicker layer is larger than that included in the other layer. Because less voltage is required to perform alternation of the liquid crystal layer between a colored state and a non-colored state as the dielectric anisotropy increases, by using this construction, the variations in the drive voltage range among the liquid crystal layers may be accurately eliminated.
In addition, the liquid crystal composition included in the liquid crystal layer with a larger dielectric anisotropy may include a liquid crystal compound that has a polar group. For the liquid crystal compound having a polar group, the liquid crystal composition may include at least one compound selected from the following group: a liquid crystal ester compound, a liquid crystal pyrimidine compound, a liquid crystal cyanobiphenyl compound, a liquid crystal cyanophenylcyclohexane compound, a liquid crystal cyano terphenyl compound, and a liquid crystal difluorostilbene compound.
Furthermore, each of the liquid crystal layers may have a mutual different thickness, and the dielectric anisotropy of the liquid crystal compound in each liquid crystal layer may be different from that in the other layers. In this way, the level of freedom in designing the liquid crystal composition included in the liquid crystal layer increases, and the light modulation characteristics required of each liquid crystal layer may be optimized.
In a sixth aspect of the present invention, a liquid crystal display comprises a plurality of liquid crystal light modulation layers stacked together, each of said liquid crystal light modulation layers including a liquid crystal layer comprising a liquid crystal composition, wherein at least two of said liquid crystal layers have different liquid crystal compositions but identical maximum drive voltages.
By having at least two liquid crystal layers that have different liquid crystal compositions but identical maximum drive voltages, drive control may be made easy while the optimal light modulation characteristics are maintained. In this liquid crystal display, the drive voltage ranges for the liquid crystal layers may be made identical. In this way, drive control is made easier.
In any of the liquid crystal displays reflecting the fifth and sixth aspects of the invention, each of the liquid crystal layers has a different liquid crystal composition. In this way, it becomes possible to provide the optimal light modulation characteristics in each liquid crystal layer, which leads to high-quality light modulation for the entire liquid crystal display having a layered construction.
In any of the liquid crystal displays reflecting the fourth, fifth and sixth aspects of the invention, the liquid crystal composition in each liquid crystal layer may include a liquid crystal compound and an additive. The kind of the additive included in the liquid crystal composition in one liquid crystal layer may be different from the kinds of the additives included in the other liquid crystal layers, and the kind of the liquid crystal compound included in the liquid crystal composition in one liquid crystal layer may be different from the kinds of the liquid crystal compositions in the other liquid crystal layers.
For the additive, a substance that includes a compound that has at least one asymmetric carbon may be used. By adding such an additive to nematic liquid crystal as a chiral agent, a liquid crystal composition that exhibits a cholesteric phase at room temperature may be obtained. By changing the amount and type of the chiral agent added, characteristics of the liquid crystal composition, such as the selective reflection wavelength, may be changed.
The additive may comprise a multichroic pigment. By using a multichroic pigment, the chromatic purity of the display of the liquid crystal layer may be improved.
The liquid crystal layer may be alternated between a selective reflection state and a pass-through state, and the liquid crystal composition may comprise one that exhibits a cholesteric phase at room temperature, for example. In this case, if the liquid crystal layers comprise three layers, i.e., a liquid crystal layer for blue color that displays blue, a liquid crystal layer for green color that displays green, and a liquid crystal layer for red color that displays red, stacked in that order from the light receiving side, high-quality multi-color images may be displayed.
The liquid crystal layer may be alternated between a state in which it absorbs light of a specific wavelength range and a pass-through state, and may comprise one that performs display based on the guest-host effect, for example. This type of display may be realized, for example, by using a liquid crystal composition comprising nematic liquid crystal to which a multichroic pigment is added as an additive. In this case, by controlling the orientation of the pigment molecules by changing the liquid crystal molecular alignment, the liquid crystal layer may be alternated between a colored state and a transparent state.
A color filter may be used between at least one pair of adjacent liquid crystal layers. By using a color filter, the chromatic purity of the display of the liquid crystal, as well as the angle of visibility, may be improved.
Each liquid crystal layer is preferably held between substrates. At least one of the substrates may be pliable. By using pliable substrates, the liquid crystal display may be made flexible. In particular, where resin film substrates are used, the liquid crystal display may be made lightweight.
Resin structures may be placed in the light modulation area between the substrates that hold each liquid crystal layer. By placing resin structures in this way, the distance between the substrates may be accurately maintained and the thickness of the liquid crystal layer may be made uniform. In addition, the substrate distance may be maintained well even if pliable substrates are used, and it is easy to increase the size of the liquid crystal display.
Each liquid crystal layer may comprise a composite film in which the liquid crystal composition is dispersed in a high-polymer matrix. If this is done, increasing the size of the liquid crystal display is easy and a good angle of visibility may be obtained.
Each liquid crystal light modulation layer may include functional films, which may have identical thicknesses. In this way, the construction of the substrates having functional films may be made identical, which makes manufacturing easier.